This invention relates to the field of orthopaedics, and in particular to an apparatus for use in external fixation.
A variety of techniques are known for holding together the parts of a fractured bone while healing is taking place. One such technique, which is most usually employed for fractures of the tibia, is external fixation. This involves passing a plurality of pins usually two or three, through each of the parts of the bone so that the pins emerge through the skin of the patient. The pins may either emerge from the skin on only one side of the bone (single-sided fixation) or they may emerge on both sides (double-sided fixation). In what follows, only single-sided fixation will be referred to, but it is to be understood that what is described applied with appropriate modifications also to double-sided fixation.
In most known forms the emerging ends of the pins are connected to a frame by adjustable clamps, and after the bone has been manipulated to reduce the fracture the clamps are tightened to hold the parts of the bone fixed with respect to one another and in the correct position. There are two main difficulties associated with this procedure. Firstly, accurate reduction of a fracture in three dimensions is very difficult and time consuming. Secondly, a frame which allows all the movements necessary for accurate reduction is of necessity complicated since a large number of lockable joints are necessary. Once reduction and fixation have been achieved a complicated and cumbersome apparatus remains attached to the patient. Systems have been designed which attempt to simplify the frame, but in these the relative movement of the pins is restricted and hence the accuracy of reduction possible is reduced.
U.K. Pat. No. 2095999 provides means by which the functions of fracture reduction and fixation can be separated from one another, so that a sophisticated apparatus can be used on a patient for fracture reduction and then replaced, after reduction has been carried out by a simple fixation device, the reduction apparatus thus being freed for use on another patient. In particular, U.K. Pat. No. 2095999 provides a fracture reduction apparatus comprising means for holding the ends of bone fixation pins, and means for rotating the said holding means about three orthogonal axes passing through a point which is, in use, located at the site of the fracture and for moving the said holding means parallel to the said axes.
The apparatus described in U.K. Pat. No. 2O95999 is capable of providing excellent results. However, it is complicated and, therefore, expensive, and it would therefore be desirable to have an apparatus which was capable of providing broadly comparable results but using a simpler and less expensive construction.
Attention is also drawn to United Kingdom Patent Specification No. 2110094A which describes a fracture reduction apparatus which includes two units each of which provides for rotation of a set of bone fixation pins about two orthogonal axes passing through the bone. The specification also refers to the possibility, though no details are given, of rotating the units about a rod, the axis of which is spaced from the bone. In contradistinction to this, as will be apparent from what is said below, each set of fixation pins used in the present invention is rotatable about three axes which all intersect one another at a point located in the bone.